Means for bounding a space for receiving pressurised gas



D. s. BLISS 3,

MEANS FOR BOUNDING A SPACE FOR RECEIVING PRESSURISED GAS Jan. 7, 1969 Sheet of- Filed July 21, 1966 INVENTOR D. S. BLISS Jan. 7, 1969 D. s. BLISS 3,420,330

MEANS FOR BOUNDING A SPACE FOR RECEIVING PRESSURISED GAS Filed July 21, 1966 Sheet 2 of 7 i T b V JNVEA/TOE D. 5. BLISS Milan, W

- D. S- BLISS Jan. 7, 1969 MEANS FOR BOUNDING A SPACE FOR RECEIVING PRESSURISED GAS Sheet Filed July 21, 1966 mwn'a/P D. 5.151.185

- i ATTORIIZEKS' D. BLISS Jan. 7, 1969 MEANS FOR BOUNDING A SPACE FOR RECEIVING PRESSURISED GAS Filed July 21, 1966 Sheet 3,420,330 MEANS FOR BOUNDING A SPACE FOR RECEIVING PRESSURISED GAS Filed July 21, 1966 D. S. BLISS Jan. 7, 1969 Sheet DYE/V701? D- 5. BLISS BY Gama non, WW1,

Jan. 7, 1969 5. ugs 3,420,330

MEANS FOR BOUNDING A SPACE FOR RECEIVING PRESSURISED GAS Filed July 21, 1966 Sheet 6 of '7 fig. 97.

[NI M701? D. S. BLIS S ATTOMEKY Jan. 7, 1969 D. s. BLISS 3,420,330

MEANS FOR BOUNDING A SPACE FOR RECEIVING PRESSURISED GAS Filed July 21, 1966 Sheet 7 of Zfo" W 5/ w w ATTOMVEYJ United States Patent 3,420,330 MEANS FOR BOUNDING A SPACE FOR RECEIVING PRESSURISED GAS Denys Stanley Bliss, Southampton, England, assignor to Hovercraft Development Limited, London, England, a British company Continuation-impart of application Ser. No. 267,695, Mar. 25, 1963. This application July 21, 1966, Ser. No. 566,948 Claims priority, application Great Britain, Mar. 27, 1962,

11,645/ 62 US. Cl. 180-128 53 Claims Int. Cl. B60v 1/18; 360v 1/16 ABSTRACT GF THE DISCLOSURE This application is a continuation-in-part of application Ser. No. 267,695 filed Mar. 25, 1963, and since abandoned and relates to means for bounding a space for receiving pressurised fluid, for example, gas. The invention is particularly applicable to gas-cushion vehicles, that is to say, to vehicles for travelling over a surface and which are supported above that surface, at least in part, by a cushion of pressurised gas formed and contained beneath the vehicle body, the vehicle-supporting cushion being bounded, at least in part, by a flexible wall depending downwardly from the vehicle body.

It is desirable that the wall should be flexible so that when the vehicle meets surface irregularities such as rocks and the like on land and waves at sea then it can deflect so as to reduce the possibility of damage to itself and to reduce the imposition of undesirable loads on the vehicle.

One form of flexible wall which has been proposed for gas-cushion vehicles comprises a continuous length of material, such as rubber, rubberised fabric and the like. However, such a flexible wall has a disadvantage in that local deflection of the wall has an overall distorting effect on the wall. Furthermore, in the event of damage to even a small part of the flexible wall it may be necessary to replace the whole of the structure.

According to the invention, means for bounding a space for receiving pressurised fluid comprises a structure forming one boundary part of the space and a flexible wall forming another boundary part of the space, the flexible wall comprising a succession of independently deflectable, flexible wall members each having an outer portion which extends away from said structure and which faces said space so as to form part of a boundary surface and a pair of side portions which extend inwardly from said outer portion towards said space, a side portion of each wall member being continguous with the adjacent side portion of a neighbouring wall member, and constraining means for constraining the wall members against deflection away from said space by the pressure of gas therein, whereby inflation of said wall members by pressurised gas, which may be from said space, urges the contiguous side portions of neighbouring wall members towards each other.

The volume of pressurised fluid may be bounded by the flexible wall only or it may be bounded by a combination of the flexible wall and fluid curtains. For example, in the case of a gas-cushion vehicle wherein the volume of pressurised fluid is the vehicle-supporting gas cushion, the flexible wall may be used to bound the upper part only of the cushion periphery, the lower part thereof being bounded by fluid curtains issuing from the bottom of the flexible wall.

When the flexible wall is fitted to a gas-cushion vehicle the wall members thereof are preferably inclined inwards towards the space occupied by the cushion (the cushion space) as this arrangement means that substantially tensile loads only are applied to the material of the wall members and thus only thin (e.g., .Ol5".030"), light (e.g. 15 oz. to 30 oz. per square yard) material can be used for construction of the wall members.

However, in the case of a gas-cushion vehicle, inward inclination of rear mounted wall members can result in the latter scooping up water or debris. Hence, according to a further feature of the invention, at least some of the wall members may have flexible wall means, for example, a flexible panel spaced inwardly from the outer portion of each such wall member and extending between the side portions of each wall member to define a space. This modification is also useful when fluid curtains are used with the wall members as the interiors of the wall members can serve as passageways for curtain forming fluid.

The invention will be understood from the following description of certain embodiments in conjunction with the accompanying drawings in which:

FIGURE 1 is a side elevation of one particular form of gas-cushion vehicle,

FIGURE 2 is a vertical cross-section, to an enlarged scale, of the front end of the vehicle illustrated in FIG- URE 1,

FIGURE 3 is a cross-section on the line IIIIII of FIGURE 2,

FIGURES 4 and 5 are views similar to that of FIG- URE 2 and illustrate the effect of certain modifications,

FIGURE 6 illustrates the effect on a vehicle in roll,

FIGURE 7 is a detail looking in the direction of the arrow VII of FIGURE 2,

FIGURE 8 is a vertical cross-section illustrating a modification of the embodiment illustrated in FIGURE 2,

FIGURE 9 is a cross-section on the line IXIX of FIGURE 8,

FIGURE 10 is a side view of another form of gascushion vehicle embodying the invention,

FIGURE 11 is a vertical cross-section, to an enlarged scale, of the front end of the vehicle illustrated in FIG- URE 10,

FIGURE 12 is a crosssection on the line XIIXII of FIGURE 11,

FIGURES 13 and 14 are vertical cross-sections similar to that of FIGURE 11 and illustrate modifications thereof,

FIGURE 15 is a cross-section on the line XV-XV of FIGURE 14,

FIGURES 16 to 18 are vertical cross-sections illustrating further modifications of the arrangement of FIG- URE 11,

FIGURE 19 is an exploded isometric view of one form of detachable mounting means for the wall members,

FIGURES 20 and 21 are vertical cross-sections of another arrangement and illustrate alternative operating conditions,

FIGURE 22 is a vertical cross-section through a further modification of the vehicle of FIGURE 10,

FIGURES 23 to 25 illustrate diagrammatically various 3 operating conditions of the arrangement illustrated in FIGURE 22,

FIGURE 26 is an exploded perspective view illustrating an arrangement providing a propelling or the like force,

FIGURE 27 is a plan view of part of the arrangement illustrated in FIGURE 26,

FIGURE 28 is a vertical cross-section through still a further modification f FIGURE 11,

FIGURE 29 is .a vertical cross-section similar to that of FIGURE 2, illustrating a further modification thereof,

FIGURE 30 illustrates a further modification of the arrangement of FIGURE 13,

FIGURE 31 illustrates the arrangement illustrated in FIGURE 2 with mechanical retracting means,

FIGURE 32 is an inverted plan of a further gas-cushion vehicle, and

FIGURE 33 is a vertical cross-section on the fore and aft axis thereof.

FIGURES 1 to 3 illustrate a gas-cushion vehicle 1 of the so-called plenum chamber type wherein the vehicle is supported above a ground surface 15 by a cushion of pressurised air formed and contained in a cushion space 8 beneath the vehicle body, the air being drawn in through side intakes 2 by engine-driven fan units 3 and fed, by way of ports 10 formed in the bottom surface 9 of the vehicle body, to the space 8 to form the pressurised cushion. The periphery of the cushion is bounded by a flexible wall 4 and the upper surface of the cushion is bounded by the bottom surface 9 0f the vehicle body.

The wall structure 4 comprises a side-by-side succession of separate independently deflectable flexible wall members 5 each comprising an outer portion 6 which extends downwardly away from the bottom surface 9 and which faces the cushion space 8 so as to form part of a boundary surface. The outer portion 6 is flanked by two side portions 7 which extend inwardly from the outer portion 6 so as to define a concavity 12, the hollow of which is presented towards the cushion space 8. A side portion 7 of each Wall member is contiguous with the adjacent side portion of a neighbouring wall member. The upper edge of each wall member 5 is attached to the bottom surface 9 of the vehicle body so that the side portions 7 serve as flexible tie means constraining the wall member against deflection away from the space 8 by pressure of the cushion therein. When the vehicle is in operation (i.e. when the cushion in space 8 has been formed) air from the cushion space enters the concavities 12 of the wall members 5 to inflate the wall members and in so doing urges the contiguous side portions 7 of neighbouring wall members towards each other to effect a cushion seal by filling the lateral boundary part of the cushion.

Each wall member 5 is formed from a single fold of flexible sheet material of substantially triangular shape. The material is neoprene-proofed nylon, the weight of which is 18 oz. per square yard and the thickness .025. The bight of the fold forms the channel-shaped concavity 12 seen in FIGURE 3 and the side portions 7, the arms of the fold. A wall member 5 has substantially square corners at its top where it is attached to the Vehicle body and a rounded form further down where it is subjected to the loading of cushion air.

The outer portion 6 of each wall member 5 (and hence the axis of the bight of the fold) slopes downwardly and inwardly towards the cushion space 8 so that the inflation loads 7 (FIGURE 2) act normal to the inner surface of this portion. The loads p have a resultant Pr acting outwardly and downwardly from midway along the portion 6, along .an imaginary line 18 extending between the extremities of attachment 16, 17 of the wall member 5 to the bottom surface 9 of the vehicle body. As the resultant Pr acts downwardly and outwardly, loads applied to the wall member 5 by inflation pressure (i.e. by cushion pressure) maintain the material of the wall member substantially in tension. This arrangement keeps the wall member taut and allows the use of thin, light (and thereby easily deflectable) materials for its construction, the materials having no substantial stiffness.

The wall member inflation loads p are transferred to the vehicle body surface 9 by way of the side portions 7 along an infinite number of lines 19 which act normal to the outer portion 6 of the wall member 5. The angle made at the bottom 14 with the inner edge 13 and the outer portion 6 is substantially 90, and this follows from arranging the wall member so that line 18 along which the resultant Pr acts extends between the extremities of attachment 16, 17 of the wall member 5 to the under surface 9.

With reference to FIGURE 4, making the angle at the bottom 14 substantially greater than 90 is a waste of wall member material as the parts of the side portions 7 shown as shaded do not take away the inflation loads 2. This is because the loads have to be carried in shear and the shear strength of the wall member material is extremely small.

With reference to FIGURE 5, making this angle substantially less than 90 will result in outward deflection, by the cushion, of the bottom 14 of the Wall member (as indicated in dotted lines) as the inflation load Pr applied to this part of the wall member cannot be transferred to the vehicle body undersurface 9. This outward deflection can be resisted by making the wall member of very shearstiff material, but as the wall member is required to be flexible, making it of stiff material affects its flexibility. In practice, with the above mentioned wall member material, the angle can vary between -90.

The preferred angle of inward inclination of the outer portion of a wall member is substantially 45 to the horizontal. This arrangement results in an economic use of wall member material.

Furthermore, when attached along the sides of a gascushion vehicle, inwardly sloping wall members 5 provide the vehicle with a substantial amount of built-in roll stability, in some cases enabling longitudinally disposed cushion-dividing means (such as the wall structure 62 of U8. Patent 3,172,494) to be dispensed with.

With reference to FIGURE 6, this is because, as the vehicle rolls to one side, the lower portions of the wall members 5 on that side flatten on the surface beneath, so increasing the effective area of the vehicle-supporting cushion. Then centre of pressure (C.P.) of the cushion is therefore displaced from its original position towards the downgoing side of the vehicle and this shift of cushion C.P. creates a restoring force which tends to correct the roll.

It has been found that inwardly inclining the wall memher 5 towards the cushion 8 at an angle of substantially 45 to the surface 15 provides a good roll stability without making the vehicle too stiff in roll for passenger comfort.

In operation, once the cushion of pressurised air is formed beneath the vehicle body, the wall members 5 are fully extended so that their bottoms are in light contact with the ground surface 15 beneath the vehicle, air excess to cushion-forming requirements escaping to atmosphere through small triangular spaces 11 between the rounded bottoms of the wall members (FIGURE 7).

In the example shown in FIGURES 2 and 3 the height h of a wall member 5 is 30 inches and the distance between the side portions 7 of each wall member is 12 inches, is. a ratio of substantially 2.5 :1. In practice a ratio of between 2:1 and 3:1 has been found to be satisfactory for a ratio of substantially less than 2:1 results in too much air escaping from the cushion space 8 by way of the spaces 11, and a ratio of substantially greater than 3:1 sometimes leads to a deflected wall member being trapped by distension of the wall members on either side. Cushion pressure in the space 8 is 20 lb. per square foot.

Rear mounted wall members 5 may, when the vehicle 1 is moving forward over water at below hump speeds, scoop up water or, when moving over land, scoop up debris. Similar effects can occur with wall members positioned at the front or sides of a vehicle when the vehicle is manoeuvring. With reference to FIGURES 8 and 9, this scooping can be reduced, or avoided, by attaching to each wall member flexible Wall means in the form of a panel of flexible material extending between the inner edges of the side portions '7 to blank off the otherwise open space between said inner edges and so define, with the remainder of the wall member, an enclosed space 21. By fitting a panel 20 to the wall member, it will also be more readily deflected by obstacles as scooping tends to resist deflection. A vent/inflation aperture 22 perforates the panel 20 to connect the space 21 with the cushion space 8 so that the wall member is readily inflated by cushion air and so that air within the wall members can escape when the wall member is deflected and not build up in pressure to make the wall member stiff.

FIGURES 10 to 12 illustrate a gas-cushion vehicle 25 wherein the vehicle-supporting cushion is contained in a cushion space 26 for the upper part of its height by a flexible wall 4 and for the remainder of its height by curtains 27 of moving air issuing from the bottoms of the wall members 5 inwardly towards the cushion space 26. The air forming the curtains 27 is ambient air drawn in through side intakes 28 on the vehicle body by engine-driven fan units 29 and delivered to a chamber 30 extending over the lower part of the vehicle body. From the chamber 30 the air is discharged (at a pressure of about twice that in the cushion space 26) from an annular port 31 formed in the bottom surface 32 of the vehicle body. The air then flows down the inner surfaces of the outer portions 6 of wall members 5 to form the air curtains 27. Initially, with the vehicle 25 at rest on the surface 15, with the wall members 5 folded beneath, air discharged from the port 31 forms the air cushion and inflates the wall members 5 and thereafter issues from the bottoms of the Wall members 5 to form the air curtains 27 which are deflected round and outwards by the pressure of the cushion of air contained in the space 26.

The flexible wall members forming the flexible wall structure of the invention can bet modified as illustrated by the way of example in FIGURES 13 to 15. FIGURE 13 illustrates a flexible wall member 5 in which the outer portion 6 thereof is curved in vertical cross-section. This provides a more gradual change in direction of the air discharged from the port 31 before it issues from the bottom of the wall member 5 in the form of the curtain 27. It will be noted that the change in cross-section results in the inflation loads p acting radially which means that the resultant Pr and line 18 radiate from the inner attachment extremity 17.

The flow of curtain-forming air down the hollow of the concavity of each wall member can, under certain conditions, intermix with cushion air to cause a power-loss. FIGURES 14 and 15 illustrate one way of avoiding or at least reducing such intermixing. In FIGURES 14 and 15, located between the side portions 7 of each wall member 5 and spaced inwardly from the outer portion 6 of the wall member, is a flexible wall means in the form of a panel 38 of flexible material which forms a nozzle 39 through which air flows from the port 31 to the bottom of the wall member.

As mentioned above, wall members may tend to act as scoops, either because of the particular position at which they are attached to a vehicle body, or due to the direction of movement of the vehicle during manoeuvring. FIG- URES 16, 17 and 18 illustrate further modifications which will avoid or at least reduce this scooping action. FIGURE 16 shows a wall member 5 identical to that shown in FIGURE 11 save that it is provided with an apertured panel 20 enclosing a space 21, as in FIGURE 8, and with an air discharge port at its bottom 14 thereof through which air outflowing from the port 31 issues to form the air curtain 27. The opening 22 can be sized so that pressure in the enclosure 21 is at substantially the same pressure as the cushion in space 26 or, alternatively, at any pressure intermediate of the pressure of the cushion and the pressure of the curtain-forming air flowing through the enclosure 21.

FIGURE 17 illustrates a flexible wall member very similar to that shown in FIGURE 16, the only difference between the two wall members being that the outer portion 6 of the former, instead of being wholly inclined, comprises an upper, substantially vertical portion 6a and a lower, inwardly inclined portion 6b, the angle of inward inclination of which is substantially 45 to the surface 15. The arrangement reduces the effective area of the cushion rather less than previously described arrangements. The portions 6a, 6b are of substantially equal length so that the line 18 associated with resultant Pr of the inflation loads coincides with the inner extremity of attachment 17. If the wall member 5 is constructed so that portion 6a is longer than portion 6b, when the wall member is inflated, there is a tendency for the lower part of the wall member to pivot upwardly, about point 17, collapsing the upper portion 6a until the effective length thereof is equal to the length of portion 6b. Hence, the wall member should be constructed so that portion 6a is equal to or longer than portion 6b.

FIGURE 18 is a further modification of the wall member 5 of FIGURE 16 and shows the wall member provided with flexible wall means in the form of a panel 5 1 of flexible material spaced inwardly from the outer portion 6 and extending between the side portions 7 to define a nozzle 51 through which air flows from the port 31 to issue from the port 45 at the bottom of the wall member 5 and form the air curtain 27.

As the flow of air forming the curtain 27 also provides air to make up losses from the cushion, substantial deflection of a number of flexible wall members of the closed form illustrated in FIGURES 16 to 18 may interfere unduly with this makeup flow were it not for air flowing to the cushion space 26 through the openings 22 in the panels 20. In the case of the wall member 5 of FIGURE 18, an additional opening, namely, opening 52 in the panel 50, is required.

It is a feature of the invention that the flexible wall members are free to deflect relative to each other. If a gound surface obstacle encountered by the vehicle 1 or 25 is thin, then only one or two wall members will be deflected whilst if the obstacle is wide several wall members will be deflected. The manner of wall member deflection is the same, whether it is on the vehicle 1 or 25. The only difference is that the vehicle 25, having an increased ground surface to vehicle body clearance by reason of the air curtains 27 can pass over taller obstacles before its wall members 5 need to deflect. When one wall member 5 of a wall structure 4 deflects, the side portions 7 of the neighbouring wall members on each side of the deflected wall member tend to be urged together so as to tend to maintain a cushion seal. As soon as the obstacle causing deflection has ceased to act on the deflected wall member, the latter is returned to its original position by its inflation pressure. If a wall member 5 is torn away by contact with an obstacle then adjacent side portions 7 of neighbouring wall members will be urged together by their inflation pressures to close off at least in part the gap left by the removed wall member.

FIGURE 19 illustrates an arrangement for mounting the wall members 5 onto the vehicle 25. The arrangement could, of course, be adapted for use on the vehicle 1 or other vehicles. With reference to the figure, the arrangement comprises a frame 60 having two side arms 61 and 62, an outer rail 63 and a cross bar 64. The upper edges of the side portions of a flexible Wall member 5 are perforated by holes 58 so as to be attachable, by lacing, to the side arms 61 and 62, the outer portion of the wall member being attachable in the same way to the outer rail 63. The outer rail 63 has a vertically extending lug 65 drilled to accommodate a bolt. The inner ends of the side arms 61 and 62 pass through holes in a support beam 66 attached to the bottom surface 32 of the vehicle body.

The side arms are first inserted in these holes and a bolt then passed through the lug 65 and screwed into the side of the vehicle body. Thus, each flexible wall member is readily attached and detached relative to the vehicle body.

Although the wall members 5 of a flexible wall have, in the above-described examples, been separate from each other, several of them can be attached to each other to form groups. The attachment between a pair of wall members would take place along the adjacent upper edges of the side portions 7 of each pair and could be achieved by stitching these edges together. Although this adaptation would not allow them, in the strict sense of the word, to remain separate," it would not interfere with their ability to deflect relative to each other.

In the arrangements wherein air curtains 27 issue from the bottoms of the flexible wall members 5, then, when a wall member is deflected by a surface obstacle, the member normally remains in contact with the obstacle and although no air curtain exists over the period of contact, this does not matter as contact between the wall member and the obstacle maintains a cushion seal. However, to prevent susbtantial leakage of cushion air in the event of the flexible wall member not being returned to its original position quickly enough by cushion pressure, means may be provided for forming a temporary air curtain external a flexible wall member 5 when the latter is deflected.

With reference now to FIGURES and 21 the wall member 5 shown therein is identical to that shown in FIGURE 17, except that the present wall member 5 does not have the flexible panel 20. Furthermore, the wall member has an enlarged upper end of portion 6a which extends into an enlarged, annular portion 72 of the chamber 30, which portion is formed by a curved surface 73 which curves round and down so that its lower edge 74- merges with the outer lip of the port 31. The upper, enlarged end of the portion 6a is attahced to a stationary air deflector 75 spaced from the wall of and disposed within the portion 72. In its normal, that is, undeflected position of the wall member 5 (FIGURE 20) the upper end of the portion 6a thereof is held in contact with the outer lip of the port 31 by air flowing from the chamber 30 where it is deflected by the deflector 75, through the port 31, to flow down the hollow of the concavity of the wall member 5 to issue from the bottom of the wall member in the form of the air curtain 27. When a succession of wall members 15 are provided, the enlarged portion 72 and also the deflector 75 can extend continuously and undivided for the length of the wall structure formed by the wall members 5.

In the wall member 5 of, say, FIGURE 17, on substantial deflection of the wall member the inner surface of the outer portion 6a thereof is caused to contact the inner lip of the port 31 and so cut off the flow of curtainforming air. However, in the present embodiment, deflection of the wall member 5 by an obstacle 70 to the same extent allows air from the chamber 3t) to flow over the back of the deflector 75 and issue from an opening defined by the outer lip of the port 31 and the exterior of the portion 6a to form a curtain 76, which curtain tends to prevent leakage of cushion air from the cushion space 27.

Flexible wall structures according to the invention can also be applied to gas-cushion vehicles in which spaced curtains of moving air are formed, and wherein variation in the relative mass flows of the curtain air is used to provide vehicle stabilising forces. FIGURE 22 illustrates one such embodiment which is a modification of the vehicle of FIGURE 10 and shows two parallel spaced apart ports 80 and 81 formed in the bottom surface 32 of the vehicle body. A succession of outer flexible wall members 5 are attached to the bottom surface 32 so that air issuing from the outer port 80 flows down the inner surfaces of their outer portions 6 to form air curtains 99 and a succession of inner flexible wall members 5 are attached to 8 the bottom surface 82 so that air issuing from the inner port 81 flows down the inner surfaces of their outer portions 6 to form air curtains 98. The ports 80, 81 are spaced from each other by structure 96 associated with the vehicle body structure 32.

Positioned in the chamber 36 is an upper flap 86 pivotally attached at its inner edge 88 to the upper surface of the chamber 30, and a lower flap 87 pivotally attached at its inner edge 89 to the bottom surface of the chamber 39. The outer edges of the flaps 226 and 87 are located by a slidable link 90 movable up and down by a rod 91.

The flaps 86 and 87 carry pins which slide in vertical slots 92 and 93 cut in the link 90. The flaps are biased by springs, not shown, to the positions shown in FIGURE 22. The slots 92 and 93 in the link 90 are so arranged that when the link is pushed downwards by corresponding movement of the rod 91, the upper flap 86 will be rotated to the position indicated by the dotted line 94 where the inner edge of the flap 86 contacts the structure 96. As the link 90 is moved downwards the pin locating the lower flap 87 remains stationary. On the link 90 being returned to its original position, the spring associated with the upper flap S6 restores the latter to its original position. Upward movement of the link 9% from the position shown in FIGURE 22 causes the lower flap 87 to rotate to the position indicated by the dotted line 95 where the outer edge of the flap 87 contacts the structure 96, the slot 92 in the link 9t) allowing the pin associated with the upper flap 86 to remain stationary.

The operation of the arrangement illustrated in FIG- URE 22 is as follows, the various positions of the flaps 86 and 87 being shown diagrammatically in FIGURES 23 to 25. With the link 98 in its normal mid-position, the flaps and 87 are in their upper and lower positions respectively, as shown in FIGURE 23. Air from the chamber 30 then flows through the ports 86 and 81, down the outer portions 6 of the wall members 5 and issues from the bottoms thereof to form air curtains 98, 99 and hence, primary and secondary air cushions in spaces 100, 161 respectively. Assuming that the mass flows of the air forming the curtains are the same, as is the case in the present example, then both curtains can support the same pressure drop. This means that the pressure difference between the spaces 10!: and 101 is the same as the pressure difference between the space 101 and the atmosphere outside the outer curtain 99, i.e. the pressure in the space 191 is half-way between the pressure at 106 and the pressure of the atmosphere external to the outer curtain 99.

If it is desired to increase the pressure in the space 101 relative to the pressure in the space 1%, the link 94) is moved upwards pivoting the lower flap 87 to its upper extreme position where the lower flap 87 assumes the position shown in FIGURE 24. In this position no air flows to the inner wall members 5, all the air in the chamber 30 flowing instead to the outer wall members. Also in this position the flaps 86, 87 form a convergent nozzle which results in an increase in velocity of the air and an increased mass flow whereby the outer curtain 99 is in-. creased in Strength and the periphery of the air cushion in space 199 extends effectively out to the outer curtain 99.

To reduce the pressure in space 101, relative to the pressure in space 100, the link is moved downwards to pivot the upper flap 86 to the position shown in FIGURE 25, all the air flowing in the chamber 30 now passing to the inner wall members 5 whereupon there is a variation in air velocity and mass flow. Should air forming the outer curtain 99 be completely shut off, the pressure in space 101 will then be the same as that of the surrounding atmosphere.

In practice, the two extreme positions of the flaps 86, 87, shown in FIGURES 24 and 25, are rarely used. There is likely to be some loss of efliciency when the flaps 86 and 87 are used to control air flow through the chamber 30 as the increase in mass flow is accompanied by losses. Even if the flow passage leading from the chamber to the ports 80 and 81 are made large enough to accept the increased mass flow without an increase in velocity, then losses still occur when the mass flow is not increased as the flow diffuses and is reduced in velocity. It is, therefore, advisable to provide a compromise by having duct cross-sections which will accept some increased flow without undue extra losses and also some reduced flow. The inner curtain 98 is likely to be affected to a lesser degree than the outer curtain 99 in the arrangement of FIGURE 22 as the flow path of the air forming the inner curtain is much shorter than the flow path of the air forming the outer curtain.

A variation in the angle of inclination of the air forming the curtains can be provided by mounting the wall members 5 so that they can be rotated relative to the vehicle body. FIGURE 26 illustrates, in perspective, a flexible wall member 5 the upper edge of which is attached to a board 106 carrying a journal ring 107 which is rotatably located by a bearing 103 attached to the bottom surface 32 of the vehicle body. The wall member 5 is rotated by a hydraulic actuator 189 through a rack 110 on the actuator which engages with a pinion 111 fixed centrally within the journal ring 107 by a spider 112. The actuator 109 is under the control of the driver of the vehicle through hydraulic signal lines 113. By positioning the wall members 5 so that their side portions 7 project inwards, each wall member as a whole being disposed normal to the periphery of the cushion as illustrated in FIGURE 27, which is a diagrammatic plan View, the air issues with a purely inward component and hence, no propulsion or like effort is provided. By rotating the wall members, as indicated by the dotted lines, an inclination having a component of direction parallel to the periphery of the cushion is given to the curtain-forming air providing a propulsive or manoeuvring thrust. As the wall members are rotated, some distortion of one side portion of each member occurs due to interference with the adjacent side portion of its neighbouring wall member. This interference affects the operation of the wall members to only a very limited extent and can be reduced, or avoided, by spacing the wall members apart a little for too large a spacing will allow air to escape between neighbouring pairs of wall members when the latter are in the positions indicated by the full lines in FIGURE 27, i.e. the positions they occupy before rotation.

FIGURE 28 illustrates a flexible wall member 5 of the form shown in FIGURE 14 which has a dust and spray deflecting device 115 attached to and extending downwardly and outwardly from the outer surface of its outer portion 6. The deflector 115 is formed by doubling over a single sheet of flexible material of substantially triangular form and is very similar to the flexible wall member 5 but rotated about attachment point 16 through 90. The deflector 115 is attached to the exterior of the outer portion 6 along the edges of the side portions 116 of the sheet. The deflector 115 is inflated by curtain air flowing away from the region of the cushion 26 and by spray and dust thrown up by this air.

A wall member 5 need not have an outer portion 6 at least the lower extremity of which inclines inwardly towards the cushion the wall member contains, but can have a portion 6, the whole of which is substantially vertically disposed, or even the whole or lower part of which inclines away from the cushion. However, this means that the line 18 on which the resultant Pr of the inflation loads lie will normally extend outside the points of attachment 16, 17, and, unless very stiff material is used for its construction, the wall member will be deflected outwardly away from the cushion by pressure of the cushion itself. One form of wall member construction which provides a substantial solution to this difliculty is illustrated in FIG- URE 29 and comprises a wall member 5 rotated clockwise about its outer attachment extremity 16 and connected to the bottom surface 9 of the vehicle 1 by triangular-shaped panel-like flexible extensions 130 attached to and extending between the bottom surface 9 and compression members or struts 131 attached to the top edges of the side portions 7 of the wall member. The struts 131 extend between attachment extremities 16 and 17a on the top edge of the wall member 5 and the inner edges 132 of the panels extend substantially normal to the struts 131 between attachment extremities 17 and 17a on the vehicle body and struts 131 respectively. The angle now made by the outer portion 6 of the wall member with the surface 15 is substantially 60". As explained above, to ensure that only substantial tension forces are applied by inflation loads to the wall member, the inner edges 13 of the side portions 7 thereof are substantially at right angles to the lower end of the portion 6 as indicated at 14. This characteristic is preserved in the present arrangement as the inflation loads acting on the portion 6 are transferred normal to the struts 131 as indicated by the dotted lines 133, and from the struts 131 to the bottom surface 9 as indicated by the dotted lines 134.

The arrangement allows an economic use of wall member material, for without the struts 131 and panels 130, in order to preserve the relationship between the inner edges 13 of the side portions 7 and the lower end of the outer portion 6, the inner edges would have had to extend substantially further into the cushion space 8, as indicated by the dotted lines 135.

The stiffness of the strut 131 can vary from being substantially rigid to having sufficient stiffness to resist the compressive forces imposed on it by the inflation pressure but able to collapse should additional forces be imposed, for example, when the wall member 5 encounters a surface obstacle.

When it is desired to form an air curtain 27 from the bottom of a wall member 5, the curtain-forming air should, for reasons of efliciency, have an initial inward direction of flow. Hence, it is preferable that at least the lower part of the outer portion 6 of a wall member 5 should have an inward inclination. On the other hand, inclining the lower part of the outer portion a inwardly towards the cushion, reduces the effective area thereof. FIGURE 30 illustrates a further modification of a wall member 5 which allows the use of an inwardly-directed flow of curtain air yet does not result in too great a loss of cushion area.

With reference to FIGURE 30, the wall member 5 illustrated therein is similar to that shown in FIGURE 29, except that it has a curved outer portion 6, the centre of curvation of which coincides with attachment point 17a. In this arrangement, the resultant line 18 extends through the centre of curvature 140 and so, from the centre 140, the inflation loads pass to the bottom surface 32 of the vehicle body by way of the inner edges 132 of of the panels 130.

FIGURE 31 illustrates an arrangement applied to the vehicle 1 wherein a wall member 5 is moved up and down in a controlled manner ahead of surface irregularities and in a vertical plane by a connecting rod connected to a hydraulic actuator 151. The actuator 151 is automatically controlled by a valve 153 which in turn is operated by a lever 154 and a rod 155 carrying a downwardly extending surface sensing member 156 which senses changes in the height of the vehicle body relative to the surface beneath. The bottom of the surface sensing member 156 contacts the surface 15 and this member can be buoyant so as to operate over both land and water surfaces. The lever 154 is pivoted at its end 157 to the outer end of a further lever 158. Lever 153 is pivoted at a position 159 intermediate of its two ends lWl'llCh is fixed, and is pivotally attached at the inner end 160 to the connecting rod 150. The lever 158 provides a feed back arrangement in that when movement of the surface sensing member 156 has operated valve 153 and thus caused the jack 151 to move the connecting rod 150 and hence the wall member 5, this movement of the connecting rod acts to close the valve 153. The movement of the connecting rod 150 and the wall member is thus kept in step with vertical movements of the surface contacting member 156 so as to maintain the bottom of the wall member in a given relationship to the surface 15.

Various combinations of wall members with and without air curtains formed from their bottoms can be used for containing vehicle-supporting cushions. FIGURE 32 which is an inverted plan and FIGURE 33, a vertical cross-section on the fore and aft axis of the vehicle illustrated in FIGURE 32, illustrate a gas-cushion vehicle 160 which has wall members 161 of the form illustrated in FIGURE 2 along each side, wall members 162 of the form illustrated in FIGURES 11 and 12 round the front, and wall member 163 of the form illustrated in FIGURE 16 across the rear. The cushion space beneath the vehicle body is divided laterally into three cushion compartments 171, 172, 173, by two laterally-extending rows of further wall members 164 of the form illustrated in FIGURE 2. The cushion space is also divided longitudinally by simple flaps or skirts 165. The air for forming the air curtains 27 is drawn in through side intakes 167 by engine-driven fan units 168 and is fed to fore and aft disposed chambers 169 which are the equivalents of the chamber 30 of FIG- URE 10. The curtain-forming air is discharged through ports 170 and the mass flows of the air are varied as shown in FIGURES to so that the centre of pressure of the vehiclesupporting cushion can be shifted fore-to-aft in order to correct any tendency of the vehicle to pitch. For example, under normal conditions the cushion compartments 171 and 173 would be of equal pressure and 172 slightly above that pressure, but if the vehicle tended to assume a nose-down attitude, the pressure of the compartment 161 would be increased and that of the compartment 163 decreased so as to create a correcting force applied to the vehicle body. If the vehicle tended to assume a nose-up attitude, the differentials of pressure would be reversed.

I claim:

1. Means for bounding a space for receiving pressurised gas, comprising a structure forming one boundary part of the space and a flexible Wall forming another boundary part of the space, wherein said flexible wall comprises a succession of independently deflectable flexible wall members each having an outer portion which extends away from said structure and which faces said space so as to form part of a boundary surface and a pair of side portions which extend inwardly from said outer portion towards said space, a side portion of each wall member being contiguous with the adjacent side portion of a neighbouring wall member, and constraining means connecting the outer portions of said wall members to said structure and acting substantially normal to said outer portions for constraining the wall members against deflection away from said space by the pressure of gas therein, whereby inflation of said wall members by pressurised gas urges the contiguous side portions of neighbouring wall members towards each other.

2. Space bounding means as claimed in claim 1 wherein said side portions constitute said constraining means.

.3. Space bounding means as claimed in claim 2 including means attaching each wall member to said structure by way of said side portions; whereby the resultant of the inflation loads acting on said outer portion does not extend outside the extremities of attachment of the wall member to said structure.

4. Space bounding means as claimed in claim 1 wherein at least the extremity of each outer portion furthest from said structure inclines inwardly towards said space.

5. Space bounding means as claimed in claim 4 wherein each outer portion is curved from one end to the other end thereof.

6. Space bounding means as claimed in claim 4 wherein means are provided for so supplying pressurised fluid to the parts of said wall members adjacent said structure that said fluid flows along the outer portions of said wall members to issue from the extremities of the wall members remote from said structure in the form of curtains of moving fluid co-operating with said wall members in bounding said space.

7. Space bounding means as claimed in claim 4 including means attaching each wall member to said structure by way of said side portions; whereby the resultant of the inflation loads acting on said outer portion does not extend outside the extremities of attachment of the wall member to said structure.

8. Space bounding means as claimed in claim 4 wherein means are provided for supplying pressurised fluid to the parts of said wall members adjacent said structure, whereby said fluid flows along the outer portions of said wall members towards the extremities of the wall members remote from said structure.

9. Space bounding means as claimed in claim 1 including flexible wall means spaced inwardly from the outer portions of each wall member and extending between the side portions thereof.

10. Space bounding means as claimed in claim 9 wherein the flexible wall means are disposed between the inner edges of the side portions.

11. Space bounding means as claimed in claim 9 wherein the flexible wall means are apertured so as to connect the interiors of the wall members with said space.

12. Space bounding means as claimed in claim 9 wherein the flexible wall means are disposed adjacent to the outer portions of the wall members so as to define nozzles therewith.

13. Space bounding means as claimed in claim 1 wherein at least one of the flexible wall members is provided with means introducing local stiffness into the side portions of the wall member.

14. Space bounding means as claimed in claim 13 wherein the local stiffening means comprise compression members carried by the side portions of the wall member and extending across the side portions towards the inner edges thereof.

15. Means for retaining a cushion of pressurised gas within a space, comprising a structure forming part of the boundary of the space and a flexible wall forming another part of said boundary, said flexible wall comprising a succession of wall members in side-by-side relation, each wall member being in the form of a single fold of flexible sheet material attached to said structure so as to project across the part of the boundary of the space which is to be closed by the flexible wall, with the axis of the bight of the fold sloping from the attached end of the wall member towards the space and with the arms of the fold projecting inwardly with respect to the space and so secured relative to said structure as to apply restraining forces in directions substantially normal to the axis of the bight, whereby said wall members when inflated are maintained in a desired configuration with the contiguous arms of adjacent Wall members distended into engagement with one another so as to fill the said part of the boundary.

16. Space bounding means as claimed in claim 15 including means attaching each wall member to said structure by way of said side portions; whereby the resultant of the inflation loads acting on said outer portion does not extend outside the extremities of attachment of the wall member to said structure.

17. A gas-cushion vehicle having a flexible wall adapted to form at least part of the lateral boundary of the gas cushion space, wherein said flexible wall comprises a succession of flexible wall members arranged in side-by-side relation along the said part of the boundary, each wall member being in the form of a single fold of flexible sheet material attached to the vehicle with the axis of the bight of the fold projecting downwardly across the gap which in operation exists between the underside of the vehicle and the surface over which it is operating and inwardly towards the cushion space, the arms of the fold being connected to the underside of the vehicle in such a way as to restrain outward deflection of the wall member under the action of the cushion pressure by applying restraining forces in directions substantially normal to the axis of the bight, the arms of the fold being distended by the cushion pressure into sealing engagement with the contiguous arms of adjacent wall members to resist escape of gas between adjacent wall members.

18. A gas-cushion vehicle as claimed in claim 17 including flexible wall means spaced inwardly from the outer portions of each wall member and extending between the inner edges of the side portions thereof.

19. A gas-cushion vehicle as claimed in claim 18 wherein the flexible wall means are apertured so as to connect the interiors of the wall members with the gas cushion space.

29. A gas-cushion vehicle as claimed in claim 17 provided with means for sensing changes in the height of the vehicle body relative to the surface over which the vehicle travels, and wall member actuating means controlled by said sensing means which operate to maintain the bottoms of said wall members in a given relationship to said surface.

21. A gas-cushion vehicle as claimed in claim 17 provided with wall member attachment means mounted on the vehicle body whereby a single wall member of the flexible wall may be detached from the vehicle without interfering with the other wall members of the wall.

22. A gas-cushion vehicle as claimed in claim 21 wherein the attachment means include a spaced-apart pair of wall member supports of elongate form to which the side portions of a wall member are attached, and means carried on the underside of the vehicle for supporting and locating said wall member support members.

23. Space bounding means as claimed in claim 17 including means attaching each wall member to said structure by way of said side portions; whereby the resultant of the inflation loads acting on said outer portion does not extend outside the extremities of attachment of the wall member to said structure.

24. A gas-cushion vehicle having a body and a flexible wall adapted to form at least part of the lateral boundary of the gas cushion space, wherein said flexible wall comprises a succession of flexible wall members arranged in side-by-side relation along the said part of the boundary, each wall member being in the form of a single fold of flexible sheet material attached to the vehicle body with the axis of the bight of the fold projecting downwardly across the gap which in operation exists between the underside of the vehicle body and the surface over which it is operating and inwardly into the cushion space, the arms of the folds being connected to the underside of the vehicle body in such a way as to restrain outward defiection of the wall member under the action of the cushion pressure by applying restraining forces in directions substantially normal to the axis of the bight, the arms of the fold being distended by the cushion pressure into sealing engagement with the contiguous arms of adjacent wall members to resist escape of gas between adjacent wall members, and means for so supplying pressurised fluid to the upper ends of the wall members that said fluid flows along the outer portions thereof to issue from the bottoms of the wall members in the form of fluid curtains cooperating with the wall members in forming the remainder of the lateral boundary of the gas cushion.

25. A gascushion vehicle as claimed in claim 24 including flexible wall means adjacent to and spaced inwardly from the outer portion of each wall member and extending between the side portions thereof so as to define nozzle passageways for the curtain-forming fluid.

26. A gas-cushion vehicle as claimed in claim 24 including a fluid supply port formed in the bottom surface of the vehicle body, inboard of and immediately adjacent to the outer portions of the wall members and means for discharging pressurised fluid through said port to flow down along said outer portions and issue from the bottoms of the wall members in the form of said fluid curtains, and means, operable on deflection of a wall member, for providing an alternative flow path for the curtainforming fluid, said alternative path being over the exterior of the outer portion of the deflected wall member.

27. A gas-cushion vehicle as claimed in claim 24 including flexible wall means attached to the exteriors of the wall members and extending downwardly towards the surface beneath the vehicle body to provide spray deflector means.

28. A gas-cushion vehicle as claimed in claim 27 wherein said flexible wall means comprise single folds of flexible sheet material attached to the wall members by the side portions of the folds.

29. A gas-cushion vehicle as claimed in claim 24 including a second flexible wall of the same construction as and spaced from the flexible wall defined in claim 24, and means for varying the relative mass flows of the fluid forming the fluid curtains associated with each of said flexible walls.

30. A gas-cushion vehicle as claimed in claim 29 including an inner port formed in the bottom of the vehicle body inboard of and immediately adjacent to the outer portions of the wall members forming one flexible wall, and an outer port formed in the bottom of the vehicle body inboard of and immediately adjacent to the outer portions of the wall members forming the other flexible wall, said means for varying the relative mass flows including a valve means for directing fluid to one or the other of said ports.

31. A vehicle for travelling over a surface and which is supported above that surface by at least one cushion of pressurised gas formed beneath the vehicle body, including a flexible wall bounding the cushion for at least part of its periphery, said wall comprising a plurality of separate, independently deflectable downwardly projecting flexible wall members attached to the lower part of the vehicle body, each wall member comprising an outer concave cushion-facing portion at least the lower part of which extends downwardly and inwardly towards the space occupied by the cushion, and two side portions extending inwardly from the cushi0n-facing portion towards the cushion space, the side portions of adjacent wall members normally being urged into contact with each other by the cushion pressure but being free to move relatively to each other when deflected, said side portions having inner edges which extend downwardly and outwardly relative to the cushion space and make a relatively large angle with the inwardly inclined part of the cushion-facing portion, whereby said side wall portions constrain said cushion-facing portion to resist an outward deflection thereof by the cushion pressure.

32. A vehicle as claimed in claim 31 wherein the side portions are attached to the lower part of the vehicle body for the whole of the top edges of said side portions.

33. Space bounding means as claimed in claim 32 including means attaching each wall member to said structure by way of said side portions; whereby the resultant of the inflation loads acting on said outer portion does not extend outside the extremities of attachment of the wall member to said structure.

34. A vehicle as claimed in claim 31 including flexible Wall means extending between the inner edges of the side portions of each wall member and extending downwards towards the bottom edge of said wall member, said flexible means sloping downwardly and outwardly relative to the cushion space.

35. A vehicle as claimed in claim 31 including means for supplying pressurised fluid to the upper part of at least one of said wall members, said one wall member being so constructed as to cause the fluid to issue from the bottom edge thereof and form a curtain of moving fluid, which assists the wall member in containing the cushion.

36. A vehicle as claimed in claim wherein the pressurised fluid flows down the inside of the outer cushionfacing portion of the wall member, the wall member including a flexible wall means positioned laterally within said wall member and extending between the side portions thereof to form with said wall member a passage through which flows the pressurised fluid.

37. A vehicle as claimed in claim 35, wherein the wall member includes flexible wall means extending between the inner edges of the side portions of said wall member and extending down towards the bottom edge of said wall member.

38. A vehicle as claimed in claim 31 wherein each of said flexible wall members includes at least one compression member extending downwards and inwards from the top of said outer cushion-facing portion towards the inner edges of said side portions, said inner edges extending substantially normal to the bottom part of said outer cushion-facing portion between said bottom part and the inner end of said compression member.

39. A vehicle as claimed in claim 31 including sensing means for sensing the height of the surface relative to the bottom of the vehicle, and means controlled by said sensing means to deflect a member and maintain the bottom edge of said member at a given relationship to said surface.

40. A vehicle as claimed in claim 31 wherein at least one of said flexible wall members includes means for stiffening the side portions of said flexible Wall member.

41. A vehicle as claimed in claim wherein said stiffening means comprise compression members having sufficient stiffness to resist compressive forces created by the cushion pressure, but collapsible when subjected to the imposition of forces additional to those created by the cushion pressure.

42. A vehicle as claimed in claim 40 wherein said stif fening means comprises substantially rigid compression members.

43. A vehicle as claimed in claim 40 wherein said stiffening means comprises at least one compression member in each side portion of the flexible wall member, each compression member extending downwards and inwards from the top of said outer cushion-facing portion towards the inner edge of said side portion, said inner edge extending substantially normal to the bottom part of said outer cushion-facing portion and between said bottom part and the inner end of said compression member.

44. Space bounding means as claimed in claim 31 in cluding means attaching each wall member to said structure by Way of said side portions; whereby the resultant of the inflation loads acting on said outer portion does not extend outside the extremities of attachment of the wall member to said structure.

45. A vehicle as claimed in claim 31 including means for supplying pressurised fluid to the upper part of at least one of said wall members, said one wall member being so constructed as to cause the fluid to flow towards the bottom edge thereof.

46. A vehicle as claimed in claim 45, wherein the wall member includes flexible wall means extending between the inner edges of the side portions of said wall member and extending down towards the bottom edge of said wall member.

47. In a device for supporting a load in spaced relationship to a surface by at least one cushion of pressurised gas formed between said surface and an opposing surface of said device, the combination therewith of a flexible wall attached to said opposing surface for containing, at least in part, said cushion of pressurised gas, said flexible wall comprising a plurality of independently deflectable flexible contiguous wall members, each wall member having an outer concave cushion facing portion and two side portions extending inwardly from said cushion facing portion towards said cushion, at least that part of the cushion facing portion of each wall member which is remote from said opposing surface being inclined inwardly towards said cushion and the side portions of each wall member having inner edges which extend inwardly and upwardly and make a relatively large angle with said inwardly inclined part of the cushion facing portion, the side portions of contiguous members normally being urged into contact with each other by the cushion pressure but being free to move relatively to each other when deflected, and means for constraining said cushion facing portion to resist outward deflection thereof by the cushion pressure.

48. Space bounding means as claimed in claim 47 including means attaching each wall member to said structure by way of said side portions; whereby the resultant of the inflation loads acting on said outer portion does not extend outside the extremities of attachment of the wall member to said structure.

49. A flexible wall structure for containing, at least in part, a cushion of pressurised gas formed between two spaced surfaces, said wall structure being attached to one of said surfaces and comprising a plurality of separate, independently deflectable flexible contiguous wall members, each wall member having an outer concave cushion facing portion and two side portions adapted to extend inwardly from said cushion facing portion towards said cushion, at least that part of the cushion facing portion of each wall member which is remote from said one surface being inclined inwardly towards said cushion and the side portions of each Wall member having inner edges which extend inwardly and upwardly and make a relatively large angle with said inwardly inclined part of the cushion facing portion, the side portions of contiguous members normally being urged into contact with each other by the cushion pressure but being free to move relatively to each other when deflected, and means for constraining said cushion facing portion to resist outward deflection thereof by the cushion pressure.

50. Space bounding means as claimed in claim 49 including means attaching each wall member to said structure by way of said side portions; whereby the resultant of the inflation loads acting on said outer portion does not extend outside the extremities of attachment of the wall member to said structure.

51. A gas-cushion vehicle having flexible Wall adapted to form at least part of the lateral boundary of the gas cushion space comprising a succession of flexible wall members arranged in side-by-side relation along the said part of the boundary, each wall member being in the form of a single fold of flexible sheet material attached to the vehicle with the axis of the bight of the fold projecting downwardly across the gap which in operation exists between the underside of the vehicle and the surface over which it is operating and inwardly into the cushion space, the arms of the fold being connected to the underside of the vehicle body in such a way as to restrain outward deflection of the wall member under the action of the cushion pressure by applying restraining forces in directions substantially normal to the axis of the bight, the arms of the fold being distended by the cushion pressure into sealing engagement with the contiguous arms of adjacent wall members to resist escape of gas between adjacent wall members, and means for supplying pressurised fluid to the upper ends of the wall members whereby said fluid flows along the outer portions thereof towards the bottoms of the wall members.

52. Means for bounding a space for receiving gas, com" prising a structure forming one boundary part of the space and a flexible wall forming another boundary part of the space and across which a differential pressure can be maintained, wherein said flexible wall comprises a succession of independently deflectable flexible wall members of inflatable form each having a lateral portion which extends away from said structure and a pair of side portions which extend away from said lateral portion and towards the region of higher pressure, a side portion of a wall member being contiguous with the adjacent side portion of a neighbouring wall member, and constraining means connecting the lateral portions of said wall members to said structure and acting substantially normal to said lateral portions for constraining the Wall members against deflection away from the region of higher pressure, whereby inflation of said Wall members urges the contiguous side portions of neighbouring wall members towards each other.

53. Space bounding means as claimed in claim 52 wherein said constraining means includes said side portions; whereby the resultant of the inflation loads acting on said lateral portion does not extend outside the extremities of attachment of the wall member to said structure.

1 8 References Cited UNITED STATES PATENTS 3,134,452 5/1964 Latirner-Needham 180128 3,211,246 10/1965 Lewis 180-127 3,254,731 6/1966 Schreiber 180-127 A. HARRY LEVY, Primary Examiner.

US. Cl. X.R. 

